The present invention relates to an error correction system for use with a length measuring device of the type comprising a scale carrier mounted to a first object, a scale fastened rigidly at first and second longitudinally spaced points to the scale carrier and longitudinally shiftable with respect to the scale carrier therebetween, and a scanning unit secured to a second object movable relative to the first object so as to scan the scale to measure the relative positions of the first and second objects.
In length measuring devices of the type described above, one well-known approach is to fasten a measuring band to a rigid measuring band carrier by means of an elastic adhesive layer, and then to fasten the two ends of the measuring band to the measuring band carrier rigidly by means of spot welds. See for example the discussion in the brochure distributed by Dr. Johannes Heidenhain GmbH entitled "Messtechnische Information", 8th Edition, March 1980. When this approach is used subsequent correction of the length of the measuring band, for example in order to correct for machine guidance errors, is no longer directly possible after the measuring band has been welded to the measuring band carrier.
German Patent DE-PS No. 25 18 745 describes a length measuring device having a rigid scale which is fastened at one end rigidly to a rigid scale carrier. The other end of the scale is fastened by means of an upsetting or stretching device to the scale carrier. This arrangement makes possible subsequent adjustments in the length of the scale in order to correct for measuring errors after the scale has been mounted to the scale carrier. However, this approach provides a disadvantage in that the disclosed structure increases the spatial dimensions of the measuring device.
German Patent DE-PS No. 27 12 421 discloses a length measuring device having a measuring band which is fastened at one end rigidly to the object to be measured. The other end of this measuring band, in contrast to the previously described system, is acted upon directly by a correction arrangement which operates to stretch the band and is fastened to the object to be measured. This approach in a similar manner to that described above makes possible a subsequent length change of the measuring band for purposes of error correction. However, this approach also presents the disadvantage of a relatively expensive construction which enlarges the spatial dimensions of the measuring device and requires a relatively large number of components and therefore relatively high assembly costs.